weight distribution bar connections

Hi.

Just a question - the saddle fitting that bolts to the A frame for weight distributing systems - has anyone else had trouble with them coming loose? I unhitched after a weekend trip and when I went to lever the saddles back up out of the way after disconnecting the chains, one of them moved upward. This is the second time this has happened and I've had to tighten them down again. Should I use a lock washer and nut to keep them in place? Could this cause a problem on the road?

Thanks

Jim